1. Field of the Invention
This invention relates to a system for processing the image information of a document after obtaining the information by optically reading the document, and, in particular, to a document image processing system for correcting the skewness of a document image obtained by reading a document to be processed.
2. Description of the Prior Art
In document image processing systems which are used in various machines such as optical character reading machines, facsimile machines, digital copying machines and the like, it is common practice to correct the skewness of a document image which is obtained by optically reading a document to be processed prior to subjecting the document image to desired processing steps. In prior art document image processing systems, use has been typically made of a pair of skew detecting marks provided on both sides of the top end portion of a document to be processed, and the amount of skew has been determined by detecting the relative positional difference between the pair of skew detecting marks in the auxiliary scanning direction, or the feeding direction of the document to be read, so as to carry out the skew correction of the document image. Such prior art systems, however, are disadvantageous because they are useless for documents without required skew detecting marks. Moreover, since the amount of skew determined by such prior art systems indicates the amount of skew of the document itself and not of the document image of the document, the skew correction tends to be unsatisfactory.